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1. What are the self-regulation characteristics of a CO2 power arc system? Why is a fine wire used for CO2 welding? Under a constant wire feed system, changes in arc length cause variations in current and melting speed; the mechanism that restores the arc length is thus the self-regulation mechanism of the power supply arc system. The finer the diameter of the welding wire used, the stronger the self-regulation of the arc, and the less spatter there is. This is the principle behind the fine welding wire used for CO2 welding. Thanks to advanced control technology, CO2 welders offer the best self-regulation of the arc and the most stable performance. 2. What is the load duty cycle of a welding machine? The load duty cycle refers to the percentage of time that the welder is under load within a specified working period. The calculation formula is: Load duty cycle = Welding machine’s loading time within the selected time period / Time period × 100%. (The manual welding time cycle is 10 minutes.) 3. What is direct connection? In DC arc welding, the wiring method in which the workpiece is connected to the positive terminal of the welder’s output, and the welding torch is connected to the negative terminal, is called the \"direct connection method\" or positive polarity. 4. What is reverse connection? In DC arc welding, the wiring method in which the workpiece is connected to the negative terminal of the welder’s output, while the welding torch is connected to the positive terminal, is called the \"reverse polarity\" method. Reverse polarity is used for alkaline electrodes (such as 507) as well as for carbon arc gouging and CO2 welding. 5. Why is the secondary output circuit in DC TIG welding connected in direct current straight polarity? Which metal materials are suitable for welding? When connected in direct current with the positive polarity, the tungsten electrode acts as the negative pole; electrons are emitted from the cathode area. Due to the low temperature, the tungsten electrode is less likely to be damaged, allowing for the use of higher welding currents. Suitable for welding carbon steel, stainless steel, copper, titanium, and refractory reactive metals such as molybdenum, niobium, and tantalum. 6. Why is AC TIG welding used for welding aluminum, magnesium, and their alloys? When connected in reverse polarity for direct current, the tungsten electrode acts as the positive pole, generating cations with high kinetic energy that strike the oxide films on the surfaces of aluminum, magnesium, and their alloys, thereby serving a cleaning function ； The tungsten electrode is in the anode area where the temperature is very high; as a result, the tungsten electrode suffers severe wear, making it impossible to use high welding currents for normal welding. By using an alternating square-wave power supply, the workpiece is heated during the positive half-cycle, while the oxide film is removed during the negative half-cycle, thereby enabling high-quality welding of aluminum, magnesium, and their alloys. 7. What is starting current (initial current)? Current for starting arcing when the arc-closing function is enabled, by pressing the welding torch switch ； Release the welding torch switch to apply the welding current. 1) During TIG welding, the starting current is lower than the welding current; it is used to preheat and guide the arc as well as the weld wire to the starting point, after which the welder’s switch is released to begin normal welding. 2) For MIG welding of aluminum, the starting current should be 20–30A higher than the welding current, in order to reduce lack of fusion at the start of welding. 3) For MIG welding of stainless steel and steel, the starting current is equal to the welding current. 8. What is arc-closing current? Current when the arc termination is set to “on” and the weld gun switch is pressed a second time ； It is generally 40-60% less than the welding current, and is used in TIG, MAG/CO2 welding to fill the crater at the end of the weld, thereby reducing crater-related defects such as crack at the weld tip. 9. What is rise time? During TIG welding, the transition time from the starting current to the welding current. During MIG welding, the time from the base current to the pulse current. 10. What is decay time? During TIG welding, it is the transition time from the welding current to the arc-off current. In MIG welding, the time for the pulse current to reach the base current level. 11. What is pulse welding current? Peak current during TIG or MIG pulsed welding. 12. What is the base welding current? Minimum current during pulsed TIG or MIG welding (adjust the welding current knob for TIG welding). 13. What is the delay in gas supply interruption time? That is, the time by which the shielding gas continues to be supplied for 0.3–5 seconds after the welding arc goes out before the supply is stopped ； Generally, for TI G welding metals such as aluminum, stainless steel, and titanium, the delay before stopping the gas supply needs to be 3–5 seconds.